1. Field of the Technology
The present disclosure relates to digital printing systems having plural tandem marking or printing engines of the type with seamed photoreceptor (P/R) belts. In such printing systems, it is common practice to invert the sheet after marking on one side in a first printing engine and for feeding the inverted sheet into a second printing engine for marking on the opposite side of the sheet to thus facilitate high speed duplex digital printing. In printing systems having plural tandem engines using photoreceptor belts with seams, it is necessary to avoid imaging on belt seams. This requires some manner of skipping pitches, a pitch defined as the space on the belt for one image, in order to avoid either placing images on belt seams or having the sheet arrive outside the timing window for sheet registration in the second engine. However, skipping pitches adversely affects printer efficiency.
2. Description of the Prior Art
A general manner of belt synchronization to avoid seams, showing the control of the belt speed of the marking devices to synchronize belts, is disclosed in U.S. Pat. No. 7,519,314 B2, assigned to the same assignee as the present disclosure. However, this technique is relatively inefficient in relation to the present disclosure. It is also shown in pending U.S. application Ser. No. 12/388,101, filed Feb. 18, 2009, now Publication No. 20100209161 by Ana P. Tooker et al, “Controlling Sheet Registration In A Digital Printing System”, to control sheet registration in a printing system by varying the dwell time of a sheet in an inverter in a first marking device and changing various transport motor speeds to time the arrival of the sheet at a second marking device. However, there is no disclosure of the need to synchronize the belts for efficient avoidance of belt seams for the productivity of the printing process. With the speeds of the two PR's no longer synchronized, the seam zones of said PR's are no longer in phase. With no understanding of the relative position of the two seam zones to each other, skipped pitches may occur in a non-optimal manner impacting customer productivity.